1. Field of the Invention
The present invention is directed to a method for correcting the gaze direction for a videophone.
2. Description of the Prior Art
The `videophoning` service is increasingly significant in the field of new telecommunication services. In forecasts for the year 2000, is assumed that, following a concentration on the business sector, the majority of broadband ISDN mainlines will be for private subscribers. However, such forecasts are not without contention and presuppose favorable boundary conditions, the question of cost playing an important role in particular.
Apart from low costs, however, the solving various ergonomic problems is also an important condition for acceptance of the videophoning service on the part of private subscribers. Visual contact during videophoning is a significant ergonomic problem.
Along with gestures and facial expression, gaze is one of the most important aspects of man's non-verbal behavior. Many sociopsychological studies attest to the importance of the gaze direction and visual contact as communicative signals (A. Kendon; "Some Functions of Gaze Direction in Social Interaction", Acta Psychologica 26 (1967), pages 1 to 47). In the case of conventional videophone terminals, the geometry of the arrangement of camera, monitor and user causes an angular error .alpha. between the gaze direction towards the monitor and the camera axis, so that true visual contact in the sense of the two parties to the call "looking each other in the eye" is not possible. Thus, in the case of an arrangement according to FIG. 1, there would be the impression that the other party is always looking slightly to the This effect becomes more pronounced at close distances between the user and the terminal. This deviation true visual contact may have the effect in videophone calls of reducing or falsifying the communicative signals of gaze direction and visual contact. However, various technical devices can permit visual contact for a videophone.
In the technical production of a videophone terminal without angular gaze error, a correction of the gaze direction can in principle be achieved by various processes (B. Kellner et al., "Bildtelefon mit Blickkontakt?" (Videophone with Visual Contact?), NTZ Vol. 38 (1985) Issue 10) which follow.
A) Use of a fixed beam splitter between camera and monitor. PA1 B) Time-division multiplexing of recording and reproduction. PA1 C) Space-division multiplexing of recording and reproduction. PA1 D) Simulation of an image recording in the axis of convergence.
A partially transparent mirror is fitted in front of the monitor in such a way that the viewer can see the monitor image through the mirror, although with reduced brightness. By means of this mirror, the camera can pick up the viewer from the direction of the monitor, permitting recording and reproduction over one axis (axis of convergence).
Reproduction of the image of the other party is undertaken by a video projector on a projection screen. The camera is located behind the projection screen and can pick up the viewer through a window provided with a light valve.
Reproduction of the image of the other party is performed by means of a video projector on a partially transparent projection screen having a reflective grid structure. The camera can pick up the subscriber at the true angle of gaze through the transparent structure of the projection screen; the range of contrast of recording and reproduction is reduced.
Reproduction of the image of the other party is undertaken by a monitor, as in the case of a conventional videophone. The viewer is recorded by means of a number of cameras from various angles of gaze at the edge of the monitor. A videoprocessor is used to calculate from the individual part-images an page which permits visual contact (J. Liu and R. Skerjanc, "Bildtelefon mit virtueller Kamera zur Herstellung des Blickkontaktes" (Videophone with Virtual Camera for Establishing Visual Contact), 12th DAGM Symposium, Oberkochen-Aalen, 1990).
Of the known processes (A-D), so far only process A with partially transparent mirrors as a fixed beam splitter has been produced. The other processes have so far not been put into practice owing to technological problems in producing a suitable light valve (B) or the projection screen with grid structure (C). In the case of process (D), it must first of all be checked whether the calculated image of a camera imagined to be in the center can represent the conditions for visual contacts sufficiently accurately. Only when the necessary computing operations are known can it be estimated to what extent calculation in real time is possible with reasonable expenditure.
All the processes specified (A to D) require considerable expenditure to make visual contact possible for a videophone, which could prevent this technology from becoming established on the market. Putting the said processes into practice requires large devices with high costs to produce poor quality images on the recording side and the reproduction side.